WASHINGTON (CNN) -- President Barack Obama told British Prime Minister Gordon Brown he was disappointed that the Lockerbie bomber had been released from jail, the White House said Thursday in a statement.

Abdelbaset Ali Mohmed al Megrahi, second from left, arrives in Tripoli, Libya, on August 21.

"The president expressed his disappointment over the Scottish Executive's decision to release convicted Pan Am 103 bomber (Abdelbeset Ali Mohmed) al Megrahi back to Libya," the White House said.

Al Megrahi, the only person convicted over the 1988 bombing that killed 270 people over Lockerbie in Scotland, was released from prison last month because he has terminal cancer.

Scottish Justice Secretary Kenny MacAskill ordered the release on compassionate grounds about eight and a half years after al Megrahi was sentenced to life in prison. MacAskill had authority over al Megrahi because the bomber was serving his sentence in Scotland, which runs its own judicial system.

Al Megrahi, 57, was diagnosed with prostate cancer last year. Declassified medical reports say the cancer has spread to his lymph nodes and skeletal system. Doctors estimated in August that he had perhaps three months to live.

The families of some of his victims opposed his release -- some because he had shown their loved ones no comparable compassion, and others because it brought to an end a legal process which they hoped would shed more light on the bombing. The U.S. government also said al Megrahi should not be freed.

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He received a hero's welcome when he returned to Libya, prompting condemnation from Obama and Brown.

Since his release, the British and Scottish governments have been forced to deny allegations he was let go in order to clear the way for British oil deals with Libya.

Al Megrahi made a brief public appearance at a hospital in Libya Wednesday, looking weak and frail.

"The overall impression was of a man very weak, unable really to engage in what was going on around him, and coughing quite violently at times," said CNN Senior International Correspondent Nic Robertson, who was able to get close and see him clearly.

"He seemed to be almost too frail to take part in this," he added. "His eyes were glazed over. His eyes closed several times during the four or five minutes he was on stage."